1. Field of the Invention
The invention relates generally to devices and methods for disinfecting water and, more particularly, to a portable, low-cost system for disinfecting water using ultraviolet light.
2. Description of the Related Art
Every day, an estimated 3,000 to 6,000 die worldwide due to infections from waterborne bacteria. Death typically results from acute dehydration, malnutrition, or other related complications. The majority of victims are young children and older people that live in economically impoverished countries. In these regions, contaminated surface water sources and poorly functioning municipal water distribution systems lead to the transmission of waterborne bacterial diseases. Although the problem is particularly bad in impoverished countries, population groups in developed countries, such as residents in remote rural areas of the United States with poor water treatment and delivery systems, are also at risk. In addition, campers and hikers who do not have access to treated water also commonly fall victim to waterborne bacterial infections.
Conventional centralized water treatment and distribution systems can be very expensive and take years to complete. Furthermore, it is often impractical to provide centralized water treatment in sparsely populated areas. Therefore, to provide the at risk groups with potable water requires innovative practical solutions such as, for example, point-of-use disinfection. In one disinfection method, ultraviolet (“UV”) radiation having wavelengths in the range of 200 to 300 nm may be used to kill disease-carrying microorganisms in water. UV radiation has been found to deactivate a broad spectrum of pathogenic contaminates from amoebic sized microorganisms to bacteria, algae and viruses. Water purification by ultraviolet radiation provides numerous advantages over other currently available water treatment methods. For example, UV water purification systems do not require chemicals nor do they require expensive filters.
Existing UV water purification systems are often large installed flow-through systems serving a large number of people. However, in recent years, a number of smaller portable UV water purification systems have become available for use by individuals. Portable UV water purification systems use fluorescent tubes for emitting UV light into the water. A quartz cover is typically provided around the fluorescent tube to protect the light source from mechanical shock and to electrically insulate the light source from the water being disinfected. Quartz covers are commonly used because it has been found that quartz is transparent at germicidal UV wavelengths, such as, around 254 nm. However, quartz covers are very expensive and thereby substantially increase the manufacturing cost.
Existing UV water purification systems also include electronic circuitry for driving the fluorescent tube. The circuitry is typically configured to drive the fluorescent tube using a “cold-cathode” striking method. In this method, a high voltage (e.g., 400-500V RMS) is applied to the anode and cathode terminals of the fluorescent tube. The voltage must be high enough to produce ionization with the anode and cathode terminals at room temperature (i.e., hence “cold-cathode”). In one common cold-cathode striking method, an H-bridge driven, capacitively tuned, step up transformer circuit is used to drive the fluorescent tube with an AC power input. Unfortunately, this type of electronic circuitry is expensive to manufacture, thereby driving up manufacturing costs and making the system prohibitively expensive for many applications. As a result, UV water purification systems and, more particularly, portable UV systems have not met with great commercial success.
Due to the complexity and high costs associated with existing UV water purification systems, an urgent need exists for an improved water purification system that requires fewer components and is easily affordable to large segments of the population. It is desirable that such a system be rugged in construction and easily transportable for disinfecting drinking water in regions wherein water purification is not available. It is also desirable that such a device be lightweight, compact and easy to use. The present invention addresses these needs.